In recent years, various fields of wireless communications have been employing an orthogonal frequency division multiplex (OFDM) system. The OFDM system is a multi-carrier system using plural narrow-band subcarriers orthogonal to each other. This system transmits a signal including subcarriers respectively modulated and having square-like frequency spectrum whose shape is a substantially square form as a whole, and thus obtains high frequency-usage efficiency. Further, the OFDM system can have a longer symbol length than a single carrier system, and thus, has a resistance to the delayed waves. By addition of guard intervals, this system obtains enhanced resistance to the multipath environment.
An orthogonal frequency division multiple access (OFDMA) system is a multiple access system in which, based on the OFDM system, each of subcarriers is assigned for a dedicated destination of information to be transmitted, thereby simultaneously transmits the information to plural destinations. In the OFDMA system, it is possible to set, for example, the number of subcarriers assigned, and the radio modulation system and transmission power for a subcarrier, in accordance with destinations of information transmitted. Under some condition, there may be a case that a specific subcarrier does not exist.
An integrated services digital broadcasting-terrestrial system (ISDB-T system), which is a Japanese standard broadcasting system for digital television, employs a band segmented transmission OFDM system (BST-OFDM system). In the BST-OFDM system, the subcarriers in the OFDM system are separated into groups called segments, and the segments are assigned on the usage basis, whereby it is possible to achieve settings (for example, radio modulation system, transmission power) appropriate for each usage.
Further, in the Long Term Evolution (LTE) system developed by the Third Generation Partnership Project (3GPP), the OFDMA system is employed for the downlink from a base station to a mobile station. And a single carrier-frequency division multiple access (SC-FDMA) system, based on a discrete Fourier transform spread (DFT-Spread) OFDM, is employed for the uplink from the mobile station to the base station.
In the SC-FDMA system, the number of subcarriers to be used varies depending on frequencies (symbol rate) of the multi-value symbol data. Thus, one transmitter can use all the subcarriers set for each frequency band allocated as a transmission band. However, the one transmitter does not always use all the subcarriers at the same time. The other transmitter can use the subcarriers that are not in use, and hence, plural transmitters can share the same transmission band at the same time, effectively utilizing the frequency resources.
Further, the multi-carrier system such as the OFDM system has a high peak to average power ratio (PAPR) in the radio signals as compared with the single carrier system, requiring radio signal circuits having much lower distortion characteristics. The SC-FDMA system applies discrete Fourier transform to sequence of multi-value symbol data corresponding to original time waveform to generate modulation information of the subcarrier (frequency spectrum information). Further, the SC-FDMA system keeps the relative frequency arrangement of the subcarriers unchanged before and after subcarrier mapping, thereby bringing the time waveform of the radio signal close to the waveform of the single carrier system. This makes it possible to reduce the PAPR thereof to a level close to the single carrier system, relaxing the low distortion performance required for the radio signal circuit.
Further, the SC-FDMA system has a characteristic in which the frequency of subcarrier to be used can be easily changed by switching the mapping of the subcarrier. With this characteristic, the LTE system enables a frequency hopping function.
Patent Document 1 describes a technique related to a transmission device employing the SC-FDMA system. The transmission device of the SC-FDMA system is characterized in that frequency response of the SC-FDMA symbol is adjusted according to the frequency selection characteristics in a propagation path between the transmission device and a reception device.